1. Field of the Invention
The present invention relates to a polymer composite material reinforced by dispersion of a rigid polymer in a thermoplastic polymer matrix at the molecular level and a method for preparing said composite.
2. Prior Art
Unique properties are generally established in a polymer material due to its high-order structure. The high-order structure is influenced by such a primary structure as molecular weight, molecular weight distribution, crystallinity, orientation and so on, particularly depends largely on its molecular structure. Therefore, there has been proposed macro fiber reinforced composite materials since the past so as to overcome the limit of mechanical properties, which occur naturally.
Examples of filament fibers having a high elastic modulus and a high strength used as a macro fiber reinforced composite material include carbon fibers, glass fibers, alamide fibers and so on. However, these fibers are usually aggregates of fibril and micro fibril and thus contain defects at each place which cause micro cracks. For example, the ends of molecular chains, micro fibrils or fibers, which are propagation paths of destruction cracks, are stressed higher than the average stress in the structure subjected to an external force, that causes concentration of the stress. And since the diameter of the filament is about 10 .mu.m, an interface bonding between the fiber and the matrix must be strong enough to distribute the external stress uniformly over oriented fibers in the matrix and draw out a possible ultimate property of the fiber .
As for these problems of the structural defects of the macro fiber and the interface bonding, the far-reaching effects of the fatal defects can be reduced and the strength can be enhanced by minuteness of the diameter. That is, the minuteness of the diameter prevents the stress from concentrating at a local part and increase its aspect ratio UD (L and D are the length and the diameter of the reinforced fiber, respectively), thereby increasing the contact area, with the result that the problem of the interface bonding with the matrix molecule can be eliminated. Therefore, it is a best mode to disperse the rigid polymer in the matrix, which mode makes a critical aspect ratio easily achieved if the molecular diameter of the rigid polymer is D, resulting in establishment of the theoretical strength of the molecule if the interface bonding between the fiber and the matrix is enough since rupture of the composite material means rupture of the covalent bond of the molecular chain in the composite material. The rigid molecular chain structure provides the resulting crystal with a molecular chain rigidity due to its molecular structure and also a high strength in the direction of the molecular chain such as the molecular chain can not be folded. A foldable chain structure usually causes a defect at the folded part. Moreover, since a non-crystal part is a propagation path of the destruction crack due to a small number of covalent bonds, the rigid polymer can improves the strength of the composite material.
Therefore, if the molecular chain of the reinforcing polymer has a rigidity over a certain limit and can be dispersed microscopically and uniformly in the matrix polymer, it is expected that a small addition of the reinforcing polymer enhances various kinds of mechanical properties without a decline of the processability.
Hitherto, based on the above idea, concepts of the polymer composite are proposed in Japanese Patent Publication Tokkosho No. 61-5500 and International Patent Domestic Publication No. Sho 55-500440. These prior polymer composites are basically made according to the method in which one polymer and the other polymer are mixed uniformly with the solvent. At the present technical level, it is very difficult to disperse and mix those polymers very uniformly in the matrix, so that we have a problem that many resulting reinforcing materials (agglomerates of the rigid polymer) often have a diameter exceeding a few microns. Further, it is disadvantageous that we can not use a polymer which is not compatible with a solvent to be used. Moreover, since the use of solvent is regulated by law from various view points at present, it is preferable to provide a non-solvent method.